Synthesis of Crystalline Black Phosphorus Thin Film on Sapphire

Abstract

Black phosphorus (BP) has recently attracted significant attention due to its exceptional physical properties. Currently, high-quality few-layer and thin-film BP are produced primarily by mechanical exfoliation, limiting their potential in future applications. Here, the synthesis of highly crystalline thin-film BP on 5 mm sapphire substrates by conversion from red to black phosphorus at 700 °C and 1.5 GPa is demonstrated. The synthesized ≈50 nm thick BP thin films are polycrystalline with a crystal domain size ranging from 40 to 70 µm long, as indicated by Raman mapping and infrared extinction spectroscopy. At room temperature, field-effect mobility of the synthesized BP thin film is found to be around 160 cm² V⁻¹ s⁻¹ along armchair direction and reaches up to about 200 cm² V⁻¹ s⁻¹ at around 90 K. Moreover, red phosphorus (RP) covered by exfoliated hexagonal boron nitride (hBN) before conversion shows atomically sharp hBN/BP interface and perfectly layered BP after the conversion. This demonstration represents a critical step toward the future realization of large scale, high-quality BP devices and circuits.

Synthesis of highly crystalline thin-film black phosphorus (BP) on 5 mm sapphire substrates is realized through the conversion from red phosphorus. A field-effect transistor fabricated on synthesized BP thin film shows field-effect mobility of around 160 cm² V⁻¹ s⁻¹ at room temperature. Red phosphorus covered by exfoliated hexagonal boron nitride (hBN) before conversion shows atomically sharp hBN/BP interface and perfectly layered BP after the conversion.

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